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Wednesday, November 26, 2014

This was prompted by various replies to Jeff's recent post (see
below), which triggered many memories of déjà vu. But it got too long, in
every relevant sense, for a single comment.

Rightly or wrongly, I think knowledge of language is an
interesting example of knowledge acquired under the pressure of experience, but
not acquired by generalizing from experience. Rightly or wrongly, I suspect
that most knowledge is of this sort. That's one way of gesturing at what it is
to be a Rationalist. So I'm curious how far the current wave of skepticism
regarding POS-arguments goes, since such arguments are the lifeblood of
Rationalism.

Once upon a time, somebody offered an argument that however people
acquire knowledge of the Pythagorean Theorem, it isn't a matter of generalizing
from observed instances of the theorem. This leads me to wonder, after reading
some of the replies to Jeff: is the Platonic form of a POS argument also
unpersuasive because (1) it is bound up in "meaty, theory-internal
constructs," and (2) the input is impoverished only relative to "an
(implicit) superficial encoding and learning algorithm"? If not, what
makes the argument that Jeff offered relevantly different? The classic POS
arguments in linguistics were based on observations regarding what certain
strings of words cannot mean, raising the question of how the relevant
constraints could be learned as opposed to tacitly assumed. What's so
theory-internal about that?

Moreover, sensible rationalists never denied that thinkers can
and often do represent certain "visible things"--drawn on the board,
or in the sand--as right triangles, and hence as illustrations of
theorems concerning right triangles. The point, I thought, was that any such
way of "encoding the data" required a kind of abstraction that is
tantamount to adopting axioms from which the theorems follow. If one uses
experience of an actual drawing to activate and apply ideas of right angles
formed by lines that have no width, then one is using experience in a
remarkable way that makes it perverse to speak of "learning" the
theorem by generalizing from experience. But of course, if one distinguishes
the mind-independent "experienceables" from overtly representational encodings--I
believe that Jeff usually stresses the input/intake contrast--then any
experience-dependent knowledge acquisition can be described as the result of
"generalizing" from encodings, given a suitably rich framework for
encodings. Indeed, given a suitably rich framework, generalizing from a single
case is possible. (It's worth remembering that we speak of both arithmetic
induction and empirical induction. But if knowledge of linguistic constraints
turns out to be more like knowledge acquired via arithmetic induction, that's
hardly a point against Rationalists who use POS arguments to suggest that
knowledge of linguistic constraints turns out to be more like knowledge
acquired via arithmetic induction.)

With enough tenacity, I guess one can defend the idea that (pace
Descartes) we learn from our encodings-of-experience that the world contains
material things that endure through time and undergo change, and that (pace
Leibniz) we generalize from observations of what is the case to conclusions
about what might be or must be the case, and that (see Dyer and Dickinson,
discussed by Gallistel and others) novice bees who were only allowed to forage
a few times in late afternoons still generalized from their
encodings-of-experience in a way that allowed them to communicate the location
of food found on the first (and overcast) morning. Put another way, one can
stipulate that all experience-dependent knowledge acquisition is learning, and
then draw two consequences: (1) POS-arguments show that a lot of learning--and
perhaps all learning--is very very unsuperficial, and (2) a huge part of the
enterprise of studying knowledge of language and its acquisition consists in
(a) repeatedly reminding ourselves just how unsuperficial this
knowledge/acquisition is, and (b) using POS arguments to help discover the
mental vocabulary in terms of which encodings of the relevant experience are
formulated. But (1) and (2) seem like chapter one and verse of Aspects.

So as usual, I'm confused by the whole debate about POS arguments.
Is the idea that with regard to human knowledge of language, but not knowledge
of geometry (or bee-knowledge of solar ephemeris), there's supposed to be some
residual plausibility to the idea that generalizations of the sort Jeff has
pointed to (again) can be extracted from the regularities in experienceables
without effectively coding the generalizations in terms of how the "data
of experience" gets encoded? If so, is there any better form of the
argument that would be accepted as persuasive; or is it that with regard to
knowledge of linguistic generalizations, the prior probability of Empiricism
(in some suitably nonsuperficial form) is so high that no argument can dislodge
it?

Or is the skepticism about POS arguments more general, so that
such arguments are equally dubious in nonlinguistic domains? If so, is there
any better form of the argument (say regarding geometry, or the bees) that
would be accepted as persuasive; or is it that with regard to knowledge of all
generalizations, the prior probability of Empiricism (in some suitably
nonsuperficial form) is so high that no argument can dislodge it?

Of course, nobody in their right mind cares about drawing a sharp
line between Rationalism and Empiricism. But likewise, nobody in their right
mind denies that there is at least one distinction worth drawing in this
vicinity. Team-Plato, with Descartes pitching and Leibniz at shortstop, uses
POS considerations to argue that (3) we encode experience and frame hypotheses
in very interesting ways, and (4) much of what we know is due to how we encode
experience/hypotheses, as opposed to specific experiences that
"confirm" specific hypotheses. There is another team, more motley,
whose roster includes Locke, Hume, Skinner, and Quine. They say that while (5)
there are surely innate mechanisms that constrain the space of hypotheses
available to human thinkers, (6) much of what we know is due to our having
experiences that confirm specific hypotheses.

To be sure, (3-6) are compatible. Disagreements concern cases, and
"how much" falls under (6). And I readily grant that there is ample
room for (6) under the large tent of inquiry into knowledge of language; again,
see chapter one of Aspects. Members of Team-Plato can agree that (6) has
its place, against the background provided by (3) and (4); though many members
of the team will insist on sharply distinguishing genuine cases of
"inductive bias," in which one of two available hypotheses is
antecedently treated as more likely, from cases that reflect knowledge of how the
relevant vocabulary delimits the hypothesis space (as opposed to admitting a
hypothesis but assigning a low or even zero prior probability). But my question
here is whether there is any good reason for skepticism about the use of POS
arguments in support of (3) and (4).

Absent a plausible proposal about how generalizations of the sort
Jeff mentions are learned, why shouldn't we conclude that such generalizations
fall under (4) rather than (6)?

Sidepoint: it's not like there is any good basis, empirical or
conceptual, for thinking that most cases will fall under (6)--or that
relegation to (4) should be a last resort. The history of these debates is
littered with versions idea that Empiricism is somehow the
default/simpler/preferable option, and that Rationalists have some special
burden of proof that hasn't yet been met. But I've never met a plausible
version of this idea. (End of sidepoint.)

I'm asking because this bears on the question of whether or not
linguistics provides an interesting and currently tractable case study of more
general issues about cognition. (That was the promise that led me into
linguistics; but as a philosopher, I'm used to getting misled.)

If people think that POS arguments are generally OK in the
cognitive sciences, but not in linguistics, that's one thing. If they think
that POS arguments are generally suspect, that's another thing. And I can't
tell which kind of skepticism Jeff's post was eliciting.

Sunday, November 23, 2014

Lately, I’ve been worried that many people – mostly
psychologists, but also philosophers, computer scientists and even linguists,
do not appreciate the argument from the poverty of the stimulus. They simply do
not see what this argument is supposed to show. This difficulty leads to
skepticism about the poverty of the stimulus and about generative syntax more
generally, which, in turn, interferes with progress towards solving the problem
of how children learn language.

An argument from the
poverty of the stimulus is based on two observations: (a) there exists a
generalization about the grammar of some language and (b) the learner’s
experience does not provide sufficient data to support that generalization over
a range of alternative generalizations. These two observations
support the conclusion that something other than experience must be responsible
for the true generalization that holds of the speakers of the language in
question. This conclusion invites hypotheses. Typically, these hypotheses have come
in the form of innate constraints on linguistic representations, though nothing
stops a theorist from proposing alternative sources for the relevant
generalization.

But a common response
to this argument is that we just didn’t try hard enough. The generalization
really is supported in the data, but we just didn’t see the data in the right
way. If we only understood a little more about how learners build up their
representations of the data, then we would see how the data really does contain
the relevant generalization. So, armed with this little bit of skepticism, one
can blithely assert that there is no poverty of the stimulus problem based only
on the belief that if we linguists just worked a little harder, the problem would
dissipate. But skepticism is neither a counter argument nor a counter proposal.

So, I’d like to issue
the following challenge. I will show a poverty of the stimulus argument that is
not too complicated. I will then show how I looked for the relevant data in the
environment and conclude that it really wasn’t there. I will then invite all
takers (from whatever field) to show that the correct generalization and none
of the alternatives really is available in the data. If someone shows that the
relevant data really was there, then I will concede that there was no poverty
of the stimulus argument for that phenomenon. Indeed, I will celebrate, because
that discovery will represent progress that all students of the human language
faculty will recognize as such. Nobody requires that every fact of language
derives from innate knowledge; learning which ones do and which ones don’t sounds
like progress. And with that kind of progress, I’d be more than happy to repeat
the exercise until we discover some general principles.

But, if the poverty of
the stimulus is not overturned for this case, then we can take that failure as
a recognition that the problem is real and that the way forward in studying the
human language faculty is by asking about what property of the learner makes the environmental data evidentiary for
building a grammar.

With that preamble out
of the way, let’s begin. Consider the judgments in 1-2, which Leddon and Lidz
(2006) show with experimentally collected data are reliable in adult speakers
of English:

(1) a. Norbert remembered that Ellen painted a picture
of herself

b.*Norbert remembered that Ellen painted a picture of himself

c.Norbert remembered that Ellen was very proud of
herself

d.*Norbert remembered that Ellen was very proud of himself

(2)a.Norbert remembered which picture of herself
Ellen painted

b. Norbert remembered which picture of himself
Ellen painted

c.Norbert remembered how proud of herself Ellen
was

d.*Norbert remembered how proud of himself Ellen
was

The facts in (1) illustrate a very simple generalization: a
reflexive pronoun must take its antecedent in the domain of the closest
subject. In all of (1a-d) only Ellen
can be the antecedent of the reflexive. Let us assume (perhaps falsely) that
this generalization is supported by the learner’s experience and that there is
no poverty of the stimulus problem associated with it.

The facts in (2) do
not obviously fit our generalization about reflexive pronouns. If we take
“closest subject” to be the main clause subject, then we would expect only (b)
and (d) to be grammatical. If we take “closest subject” to be the embedded
subject, then we expect only (a) and (c) to be grammatical. And, if we take
“closest subject” to be underspecified in these cases, then we expect all of
(a-d) to be grammatical. So, something’s gotta give. What we need is for the
“closest” subject to be Ellen in
(c-d), but not (a-b). And, we need closest subject to be underspecified in
(a-b) but not (c-d). We’ll get back to a way to do that in a moment.

But first we should
see how these patterns relate to the poverty of the stimulus. Leddon and Lidz
(2006) also showed that sentences like those in (2) are unattested in speech to
children. While we didn’t do a search of every sentence that any child ever
heard, we did examine 10,000 wh-questions
in CHILDES and we didn’t find a single example of a wh-phrase containing a reflexive pronoun, a non-reflexive pronoun
or a name. So, there really is no data to generalize from. Whatever we come to
know about these sentences, it must be a generalization beyond the data of
experience.

One might complain,
fairly, that 10,000 wh-questions is
not that many and that if we had looked at a bigger corpus we might have found
some with the relevant properties. We did search Google for strings containing wh-phrases like those in (2) and the only hits we got were example
sentences from linguistics papers. This gives us some confidence that our
estimate of the experience of children is accurate.

If these estimates are
correct, the data of experience appears to be compatible with many
generalizations, varying in whether Norbert,
Ellen or both are possible
antecedents in the (a-b) cases, the (c-d) cases or both. With these possibilities, there are 8
possible patterns. But out of these eight, all English speakers acquire the
same one. Something must be responsible for this uniformity. That is the extent
of the argument. It doesn’t really have a conclusion, except that something
must be responsible for the pattern. The argument is merely the identification
of a mystery, inviting hypotheses that explain it.

Here’s a solution that
is based on prior knowledge, due to Huang (1993). The first part of the
solution is that we maintain our generalization about reflexives: reflexives
must find their antecedent in the domain of the nearest subject. The second part capitalizes on the difference between (2a-b), in which the wh-phrase is an argument of the lower verb, and (2c-d), in which the wh-phrase is the lower predicate itself. In (2a-b), the
domain of the nearest subject is underspecified. If we calculate it in terms of
the “base position” of the wh-phrase, then the embedded subject is the nearest
subject and so only Ellen can be the
antecedent. If we calculate it in terms of the “surface position” of the wh-phrase, then the matrix subject is
the nearest subject. For (2c-d), however, the closest subject is the same, independent of whether we interpret the wh-phrase in its "base" or "surface" position. This calculation of closest subject follows from the Predicate Internal Subject Hypothesis (PISH): The predicate carries information about its subject wherever it
goes. Because of PISH, the wh-phrase [how proud of
himself/herself] contains an unpronounced residue of the embedded subject
and so is really represented as [how Ellen
proud of himself/herself]. This residue (despite not being pronounced)
counts as the nearest subject for the reflexive, no matter where the predicate
occurs. Thus, the reflexive must be bound within that domain and Ellen is the only possible antecedent
for that reflexive. So, as long as the learner knows the PISH, then the pattern
of facts in (2) follows deductively. The learner requires no experience with
sentences like (2) in order to reach the correct generalization.

Now, this argument
only says that the learner must know that the predicate carries information
about its subject with it in the syntax prior to encountering sentences like
(2). It doesn’t yet require that knowledge to be innate. So, the poverty of
the stimulus problem posed by (2) shifts to the problem of determining whether
subjects are generated predicate internally.

Our next question is
whether we have independent support for PISH and whether the data that supports
PISH can also lead to its acquisition. I can think of several important
patterns of facts that argue in favor of PISH. The first (due, I believe, to
Jim McCloskey) concerns the relative scope of negation and a universal
quantifier in subject position. Consider the following sentences:

(3)a.Every
horse didn’t jump over the fence

b.A fiat
is not necessarily a reliable car

c.A fiat
is necessarily not a reliable car

The important thing to notice about these sentences is that
(3a) is ambiguous but that neither (3b) nor (3c) is. (3a) can be interpreted as
making a strong claim that none of the horses jumped over the fence or a weaker
claim that not all of them jumped.This ambiguity concerns the scope of negation. Does the negation apply
to something that includes the universal or not? If it does, then we get the
weak reading that not all horses jumped. If it does not, then we get the strong
reading that none of them did.

How does this scope
ambiguity arise? The case where the subject takes scope over negation is
straightforward if we assume (uncontroversially) that scope can be read
directly off of the hierarchical structure of the sentence. But what about the
reading where negation takes wide scope? We can consider two possibilities.
First, it might be that the negation can take the whole sentence in its scope
even if it does not occur at the left edge of the sentence.But this possibility is shown to be
false by the lack of ambiguity in (3c). If negation could simply take wide
scope over the entire sentence independent of its syntactic position, then we
would expect (3c) to be ambiguous, contrary to fact. (3c) just can’t mean what
(3b) does. The second possibility is PISH: the structure of (3a) is really (4),
with the struck-out copy of every horse
representing the unpronounced residue of the subject-predicate relation:

(4)every horse didn’t [every horse] jump
over the fence

Given that there are two positions for every horse in the representation, we can interpret negation as
either taking scope relative to either the higher one or the lower one.

Is there evidence in
speech to children concerning the ambiguity of (3a)? If there is, then that
might count as evidence that they could use to learn PISH and hence solve the
poverty of the stimulus problem associated with (2).Here we run into two difficulties. First, Gennari and
MacDonald (2005) show that these sentences do not occur in speech to children
(and are pretty rare in speech between adults). Second, when we present such
sentences to preschoolers, they appear to be relatively deaf to their ambiguity.
Julien Musolino and I have written extensively on this topic and the take away
message from those papers is (i) that children’s grammars can generate the
wide-scope negation interpretation of sentences like (3a), but (ii), it takes a
lot of either pragmatic or priming effort to get that interpretation to reveal
itself. So, even if such sentences did occur in speech to children, their
dominant interpretation from the children’s perspective is the one where the
subject scopes over negation (even when that interpretation is not consistent
with the context or the intentions of the speaker) and so this potential
evidence is unlikely to be perceived as evidence of PISH. And if PISH is not
learned from that, then we are left with a mystery of how it comes to be
responsible for the pattern of facts in (2).

A second argument (due
to Molly Diesing) in favor of PISH concerns the interpretation of bare plural
subjects, like in (5):

(5)Linguists are available (to argue with)

This sentence is ambiguous between a generic and an
existential reading of the bare plural subject. Under the generic reading, it
is a general property of linguists (as a whole) that they are available. Under
the existential reading, there are some linguists who are available at the
moment.

Diesing observes that
these two interpretations are associated with different syntactic positions in
German. The generic interpretation requires the subject to be outside of the
verb phrase. The existential interpretation requires it to be inside the verb
phrase (providing evidence for the availability of the predicate-internal
position crosslinguistically). So, Diesing argues that we can capture a cross-linguistic
generalization about the interpretations of bare plural subjects by positing
that the same mapping between position and interpretation occurs in English.
The difference is that in English, the existential interpretation is associated
with the unpronounced residue of the subject inside the predicate. This is not
exactly evidence in favor of PISH, but PISH allows us to link the German and
English facts together in a way that PISH-less theory would not. So we could
take it as evidence for PISH.

Now, this one is a bit
trickier to think about when it comes to acquisition. Should learners take
evidence of existential interpretations of bare plural subjects to be evidence
of PISH? Maybe, if they already know something about how positions relate to interpretations.
But in the end, the issue is moot because Sneed (2007) showed that in speech to
children, bare plural subjects are uniformly used with the generic
interpretation. How children come to know about the existential readings is
itself a poverty of the stimulus argument (and one that could be solved by antecedent
knowledge of PISH and the rules for mapping from syntactic position to semantic
interpretation). So, if we think that the facts in (2) follow from PISH, then
we still need a source for PISH in speech to children.

The final argument
that I can think of in favor of PISH comes from Jane Grimshaw. She shows that
it is possible to coordinate an active and a passive verb phrase:

(6)Norbert insulted some psychologists and was
censured

The argument takes advantage of three independent
generalizations. First, passives involve a relation between the surface subject
and the object position of the passive verb, represented here by the invisible
residue of Norbert:

(7)Norbert was censured [Norbert]

Second, extraction from one conjunct in a coordinated
structure is ungrammatical (Ross’s 1968 Coordinate Structure Constraint):

(8)*Who did Norbert criticize the book and Jeff
insult

Third, extraction from a conjunct is possible as long as the
extracted phrase is associated with both conjuncts (Across The Board
extraction):

(9)Who did Norbert criticize and Jeff insult

So, if there were no predicate internal subject position in
(6), then we would have the representation in (10):

(10)Norbert [VP insulted some
psychologists] and [VP was censured [Norbert]]

This representation violates the coordinate structure
constraint and so the sentence is predicted to be ungrammatical, contrary to
fact. However, if there is a predicate internal subject position, then the
sentence can be represented as an across the board extraction:

(11)Norbert [VP[Norbert]
insulted some psychologists] and [VP was censured [Norbert]]

So, we can understand the grammaticality of (6)
straightforwardly if it has the representation in (11), as required by PISH.

Do sentences like (6)
occur in speech to children? I don’t know of any evidence about this, but I
also don’t think it matters. It doesn’t matter because if the learner
encountered (6), that datum would support either PISH or the conclusion that
movement out of one conjunct in a coordinate structure is grammatical (i.e,
that the coordinate structure constraint does not hold). If there is a way of
determining that the learner should draw the PISH conclusion and not the other
one, I don’t know what it is.

So, there’s a
potential avenue for the stimulus-poverty-skeptic to show that the pattern in
(2) follows from the data. First show that data like (6) occurs at a reasonable
rate in speech to children, whatever reasonable means. Then show how the coordinate
structure constraint can be acquired. Then build a model showing how putting
(6) together with an already acquired coordinate structure constraint will lead
to the postulation of PISH and not to the discarding of the coordinate
structure constraint. And if that project succeeds, it will be party time; we
will have made serious progress on solving a poverty of the stimulus problem.

But for the moment, the
best solution on the table is the one in which PISH is innate. This solution is
the best because it explains with a single mechanism the pattern of facts in
(2), the ambiguity of (3), the interpretive properties of (5) and its German
counterparts, and the grammaticality of (6). And it explains how each of these
can be acquired in the absence of direct positive evidence. Once learners
figure out what subjects and predicates look like in their language, these
empirical properties will follow deductively because the learners will have been
forced by their innate endowment to build PISH-compatible representations.

One final note. I am
confident that no stimulus-poverty-skeptics will change their views on the
basis of this post (if any of them even see it). And it is not my intention to
get them to. Rather, I am offering an invitation to work on the kinds of
problems that poverty of the stimulus arguments raise. It is highly likely that
the analyses I have presented are incorrect and that scientists with different
explanatory tastes would follow different routes to a solution. But we will all
have a lot more fun if we engage at least some of the same kinds of problems
and do not deny that there are problems to solve. The charge that we haven’t
looked hard enough to find out how the data really is evidentiary is hereby
dismissed. But if there are stimulus-poverty-skeptics who want to disagree
about something real, linguists are available.

Saturday, November 22, 2014

I recently heard a talk by Elissa Newport, which reviewed
some current thinking on brains and language. It led me to a question. Let me
back into it.

Brains it seems are quite plastic. What this means is that
if a part of the brain usually tasked with some function is incapable of so
performing (e.g. it has been insulted in some way (or even removed (quite an
insult!)) other parts of the brain can pitch in to substitute. If the insult is
early enough (e.g. in very young kids) the brain substitutes for the lost brain
parts are so good that nary a behavioral deficit is visible, at least to the
untrained eye (and maybe even to the experts). So, brains are plastic. The
limiting case of plasticity is the equipotentiality thesis
(ET); the idea that any part of the brain can substitute functionally for any
other part.

Now one can imagine how were ET true, one might be led to
conclude that minds are also equipotential in the sense that the computations
across cognitive domains must be the same. In other words, it strikes me that
ET as a brain thesis leads to General Learning theory as a psychological
thesis. Why? Well, on the assumption that minds are brains when viewed
computationally, then there would be little surprise were any part of the brain
able to compute what any other part could if in fact brains only did one kind
of computation.

Conversely, if brains are not fully labile (e.g. if they had a more modular design) then this
would suggest that the brain carries out many distinct kinds of computation and
that some parts cannot do what other parts do. In other words, the reason that
they are not fully labile is that they differ computationally. I mention this
because it appears that current wisdom is that brains are not completely equipotential. So, though it is true that brains are
not entirely fixed in function, it also seems to be the case that there are
limits to this. Elissa reported, for example, that language function, which is
generally lateralized in the left, migrates to the analogous place in the right
hemisphere if the left side is non-functioning. In other words it moves to the
same place but on the other side. It cannot, it seems, move just anywhere (say
to the hippocampus (by far my favorite word in neuroscience! I makes me think
of a university version of this).
That the language slack left by the left hemisphere is taken up by the same
place in the right hemisphere makes sense if these areas are specialized and
this makes sense if they execute their own unique brand of computations.

Or at least that’s the way it seems to me at first blush. So
here’s my question: is that the way it seems to you too? Can we argue from
brain “modularity” against general learning? Or put another way; does a mind
that uses general learning imply a brain that is equipotential and one that is
not fully plastic argue in favor of mental modules?I feel that these notions are linked, but I
have not been able to convince myself that the link is tight.

Let me add one more point: even modularists could concede
that different parts of the mind use partially overlapping cognitive operations.
What is denied is that it is all the same all the way down.But let’s forget these niceties for now. What
I want to know concerns the pure case: does brain modularity imply mental
modularity and vice versa? Or are the two conceptions entirely unrelated?

Friday, November 21, 2014

Multidominant
structures (doubly rooted structures of the kind given in (1)) have been invoked
as a solution to a number of both empirical and theoretical puzzles.

(1)XPYP

/\/\

X ZP Y

The idea
that such structures exist spans several decades and frameworks, going back at
least to the seventies and the work of Sampson (1975) on raising and control and
Williams (1978) on Across-the-Board wh-questions. Since then, many different
mechanisms have been proposed to generate such structures, including (but not
limited to): factorization of Williams (1978), Parallel Merge of Citko (2005), behindance-Merge
of De Vries 2005, grafting of Van Riemsdijk (2000, 2006a,b), banyan trees of Svenonius
(2005), sharing of Gračanin-Yuksek (2007), union of phrase markers of Goodall (1987),
node contraction of Chen-Main (2006) and tree linking of Gärtner (2002). Interestingly,
while the issue of linearization and interpretation of multidominant structures
has received a fair amount of attention in the literature, the very fundamental
issue of how to diagnose a multidominant structure has not. We have reliable
ways to diagnose A versus A-bar positions, heads versus phrases, specifiers
versus complements, covert versus overt movement; what still seems to be
lacking is an adequate diagnostic (or set of diagnostics) of multidominance, something
akin to crossover as a diagnostic of A-bar dependencies.

Explication

The
landscape of multidominance is quite diverse and includes both coordinate and
non-coordinate structures, as evidenced by the far from complete list of
constructions (coordinate ones in (2) and non-coordinate ones in (3)) that have
been analyzed in a multidominant fashion.For the
purpose of the question of how to diagnose multidominance, it is immaterial
whether a multidominant analysis is the correct one for all of them or just a
subset thereof; all that matters is that the grammar allows such structures. Simply
put, if they exist, we need to know how to find them.

A natural
way to proceed in the search for a reliable multidominant diagnostic (or set of
diagnostics) is to ask what property (or set of properties) characterizes these
constructions to the exclusion of others. Let us thus look at some that at
various times been associated with multidominance. Intuitively, coordination might seem like a plausible
candidate. After all, the two conjuncts in a coordinate structure are parallel.
Thus perhaps multidominance is a way to capture this parallelism. However, it
is clear that it cannot be one due to the simple the fact that there do exist
non-coordinate multidominant structures, i.e. the ones given in (3). Likewise, ellipsis cannot be the right diagnostic,
in spite of the intuitive appeal of the idea that perhaps what (some) cases of
ellipsis involve is the non-pronunciation of one occurrence of the multiply
dominated element. While movement is
sometimes analyzed in a multidominant fashion, not all of the constructions in
(2-3) involve movement. Similarly, while parentheticals
of various types (appositives, amalgams) have been claimed to involve
multidominance, there exist enough multidominant yet non-parenthetical constructions
to be doubtful of a one-to-one correlation between the two.

What
the multidominant constructions listed in (2-3) seem to have in common is the
idea (or intuition) that a single element has to simultaneously fulfill the
requirements imposed on it by the two elements between which it is shared. In
other words, it has to match them in some relevant sense. If so, could matching
be a diagnostic we are after? In order to answer this question, we need to
further ask what kind of matching multidominant structures require, and what
kinds of mismatches they tolerate (if they tolerate mismatches at all). If we
limit our attention to constructions in which a nominal element is shared
between two nodes, the question becomes whether this shared nominal has to
match both in morphological case, Abstract case, thematic role, or (relative)
thematic prominence. Logically speaking, mismatches could be due to syncretism
effects, proximity effects (or the reverse, anti-proximity effects) or
hierarchy effects. The ameliorating effects of case syncretism have been
documented pretty well in the relevant literature. However, it is not the case
that mismatches due to factors other than syncretism are never tolerated. Citko
(2011), for example, points out that in Polish ATB wh-questions tolerate
mismatches only with syncretic forms, whereas Right Node Raising tolerate
mismatches that suggest proximity is at issue, as shown by the contrast between
the ATB question in (4a) and the RNR construction in (5b). In both of them, the
verbs inside the two conjuncts impose different case requirements on their
objects: the verb lubić ‘like’ requires
accusative case whereas the verb ufać
‘trust’ requires dative case. Furthermore, in both of them the object of
these two verbs (bolded in (4a-b)) is shared between the two clauses. Interestingly,
in the ATB case, neither the accusative nor the dative form of the shared
(fronted) wh-pronoun yields a grammatical result, whereas in the RNR case, the
dative form of the shared object is possible.

(4) a. *Kogo/*komuJanlubiaMariaufa? [Polish]

who.acc/who.datJan likesandMariatrusts

‘Who
does Jan like and Maria trust?’atb question

b.JanlubiaMaria ufatej koleżance/*tȩ koleżankȩ z pracy.

Jan likes and Maria truststhis.dat
friend.dat/this friend.acc from work

‘Jan
liked and everyone avoided this friend from work.’RNR

The fact
that not all multidominant constructions are subject to the same kind of case
matching requirement casts doubt on the correlation between multidominance and
matching, and, consequently, on matching as a multidominance diagnostic. Thus,
the search for a reliable diagnostic of a multidominant structure continues.